The developmental biology and differentiation of higher eukaryotes require many genes to be subject to multiple control mechanisms which regulate the time of expression, the tissues in which it occurs, and even the physical pattern of the cells in which the gene is active. We will approach the molecular basis of these mechanisms using the white (w) gene of Drosophila and its interactions. This gene, most intensively studied genetically, is a unique system to study specificity of expression, dosage compensation: the sex specific regulation which affects X chromosome genes and transvection. This last phenomenon depends on the zeste (z) locus and affects the white gene and at least two other loci, bithorax (BX-C) and decapentaplegic (dpp), of fundamental developmental importance. We will study these mechanisms by analyzing the effects of an array of mutants on white gene expression, its specificity and distribution, using Northern blots, S1 mapping, assays of w-product, and in situ detection in thin sections from different developmental stages. We will dissect the functions of the regulatory region using P-mediated transformation to reintroduce altered versions of the w gene into flies. We have cloned and will complete the analysis of the zeste gene, including the isolation of its product. The interaction of the z-product with chromosomes and their constituents will be explored in situ. In particular, we will look at its interaction with the DNA of its targets in w, BX-C, and dpp loci. The mode of action of the z-product will be analyzed also using mutations in suppressor of zeste loci. We will then attempt to clone these loci which suggest an involvement of zeste in vital cellular processes. The analysis of insertional mutants in w and z will also be continued to study their effects on transcription, termination, and splicing. The pursuit of one of these, w-a and a second site suppressor mutation promises to lead us to the mechanism of transcription termination.